Typically, multi-layer circuit boards are formed from a plurality of layers of various materials. The materials may be electrically insulating or electrically conducting. Typically, the layers are formed and various materials are deposited on the surface of one or more layers and/or various materials are introduced into portions of the various layers. Additionally, various structures, such as holes, may be formed through one or more of the layers. Furthermore, circuitization may be formed on surface(s) of the layers. After forming the layers, the layers may then be assembled into a multi-layer structure.
Often, it is important that it is known where the layers are relative to each other in the multi-layer structure. Also, it may be important to know where structures in and/or on the layers are relative to structures in and/or on other layers in the multi-layer structure. For example, when forming structures such as holes, for example, plated through holes, in the multi-layer structure, it may be important to know where the various layers, and structures formed in and/or on the layers, are relative to each other to ensure that the through holes are located in the correct position and/or an optimal position for functioning of the circuit board.
In the past, alignment, or registration, of layers of multi-layer circuit boards has been achieved through a variety of means. For example, X-rays have been used to detect the placement of various features in and/or on layers of multi-layer circuit boards. Additionally, physical means have been utilized, such as drilling holes in each layer of a multi-layer circuit board and then stacking the circuit boards on a pin. Additionally, indentations have been formed in the sides of circuit board layers to align the layers. Such methods can be costly, inaccurate, and wasteful of materials.